This application claims priority under 35 U.S.C. xc2xa7 119 to Swiss application number 2002 0427/02, filed Mar. 12, 2002, the entirety of which is incorporated by reference herein.
The present invention relates to the tensioning of a winding of a stator, in particular a generator stator of a power plant.
A conventional stator, in particular a generator stator of a power plant, consists of a core and a winding comprised of multiple winding bars. Such winding bars are designed with the ends thereof extending out from the stator core on at least one axial front side of the latter, and are flexed and joined together to form a winding head at the front side of the core, which head extends in a funnel or cone shaped manner with increasing distance from the core. To operate the stator, the winding head must be braced, that is axially post-tensioned, at the core in the axial direction of the stator. Further, it is necessary to bias the winding head radially inwardly. Such tensioning of the winding head is necessary in order to allow for the absorption of electrodynamic forces that occur during operation. Conventionally, the desired tensioning of the winding or winding head is effected at the time of manufacture of the stator. However, during operation of the stator settling and other similar phenomena may occur which can adversely affect the tension applied to the winding or winding head.
The present invention provides a remedy for this. The invention, as set forth in the claims, points to a solution for the problem of tensioning a stator winding or a winding head, which is better able to ensure that a desired, in particular, lasting tension is maintained.
The present invention is based on the general concept of bracing the winding head against winding supports using pressure spring elements, the winding supports being uniformly distributed about the circumference of and axially supported on the front side of the core. With the aid of the pressure spring elements it is possible to achieve the desired radial, inwardly directed tensioning of the winding head. Such uniform arch tension results advantageously in a permanent form closure between the winding head and the support means. The winding supports are arranged on the winding head so as to be able to move perpendicularly relative to the outer side of the winding head. Thus, the device according to the present invention is able to transfer the desired tension force from the winding supports to the winding head, even when the winding head contracts or expands in a radial direction due to settling, thermal expansion or the like. The shape of the winding head changes essentially perpendicularly to the outer side thereof and thus in the direction of force applied by the pressure spring elements, such that the latter are able to compensate for the relative movement between winding head and winding supports. Using pressure spring elements in the process that have a relatively flat spring characteristic can ensure that a change in length of the spring causes only a minimal change in tension force, that is, the pressure force of the pressure spring elements is virtually unaffected by a change in the relative position of the winding supports and winding head.
With the arrangement of the support means on the winding head in accordance with the present invention, that is, the placement of three components by means of pressure spring elements, it is possible to inhibit relative movement of the support means and the winding head under all operating conditions.
In one advantageous embodiment at least one of the pressure spring elements can have a first guide element with a central sleeve, a second guide element with a central, axially adjustable bolt within the sleeve, and a spring assembly comprised of multiple disk- or plate-shaped springs and arranged axially between the guide elements and concentrically to the sleeve. A pressure spring element of this kind is especially compact in design and enables the transfer or introduction of particularly strong pressure forces.
In a further modification, the pressure spring element may also include at least one spacer element arranged axially between the spring assembly and one of the guide elements and concentrically to the sleeve. With the aid of such a spacer element it is possible when installing the pressure spring element to vary the bias that the pressure spring element, when installed, transfers between the winding supports and the winding head. Moreover, with the aid of spacer elements of this type, it is possible, e.g. during inspections or maintenance work, to reset the bias of the pressure spring elements, in which the spacer element mounted in each is replaced with another spacing element of a different plate thickness.
It is expedient to affix each of several or all winding supports to the front side of the core by means of at least one axially tensioned plate spring, wherein all of the winding supports are arranged on the front side of the core in such a way that they are movable in a direction axial to the front side of the core. This design ensures that during axial expansion of the winding bars, the winding supports are able to yield to the concomitant axial shift of the winding head with no negative effect to the radial tension applied to the latter.
Additional substantive features and advantages of the present invention are set forth in the drawings and figure descriptions with reference to the drawings.